This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-183247, filed Jun. 29, 1999 the entire contents of which are incorporated herein by reference.
The present invention relates to a toroidal type continuously variable transmission mounted in a vehicle such as an automobile.
A toroidal type continuously variable transmission described PCT National Publication No. 6-502476 is a known example of a transmission that is mounted in a vehicle such as an automobile. The transmission of this type comprises an input shaft rotatable by means of a drive source that includes an engine, an input disk rotatable integrally with the input shaft, an output disk opposed to the input disk, power rollers arranged between the input and output disks, and a push mechanism for pressing at least one of the disks toward the other. As the input and output disks are pressed against the respective traction surfaces of the power rollers by the push mechanism, the rotation of the input disk is transmitted to the output disk through the power rollers. As the angle of inclination of the power rollers, which are rockably arranged between the input and output disks, changes, the reduction ratio of the toroidal type continuously variable transmission changes.
In some cases, a loading cam mechanism may be used as the push mechanism. The loading cam mechanism comprises a loading cam mounted on the input shaft and a cam roller in contact with the cam. The loading cam, which is located behind the input disk, is rotated by means of the drive source that includes the engine. The cam roller is located between the loading cam and the input disk and is rotatable around an axis that extends at right angles to the axis of the input shaft. When the drive source rotates the loading cam, the cam roller presses the input disk toward the output disk.
The loading cam mechanism presses the input disk toward the output disk with a push force proportional to a torque from the drive source that is applied to the input shaft. Since the loading cam mechanism mechanically presses the input disk in response to only the input torque from the drive source, there is no necessity for computer control. Thus, the toroidal type continuously variable transmission using the loading cam mechanism has an advantage over the one that uses a hydraulic loading mechanism (mentioned later) in being simpler in construction.
The efficiency of power transmission between the input and output disks and the power rollers varies depending on various conditions, such as the input torque from the drive source, gear ratio of the toroidal type continuously variable transmission, rotational frequency of the input disk, temperature of the a lubricant, etc. In the case where the loading cam mechanism is used as the push mechanism, however, the push force is settled without regard to the aforesaid conditions including the gear ratio, rotational frequency, lubricant temperature, etc. Depending on these conditions, therefore, the loading cam mechanism sometimes may fail to press the input and output disks with an optimum push force.
FIG. 4 shows the relation between a push force Fac generated by the loading cam mechanism of the half-toroidal type continuously variable transmission and an appropriate push force Fan1. If the input torque from the drive source is fixed, the push force Fac generated by the loading cam mechanism is substantially fixed despite the change of the gear ratio, as shown in FIG. 4. On the other hand, the appropriate push force Fan1 is represented by an upwardly convex curve. FIG. 5 shows the relation between the push force Fac generated by the loading cam mechanism of the full-toroidal type continuously variable transmission and an appropriate push force Fan2. The lower the gear ratio, the smaller the appropriate push force Fan2 is, as shown in FIG. 5.
Thus, in the case of the half-toroidal type continuously variable transmission that uses the loading cam mechanism, the generated push force Fac is greater than the appropriate push force Fan1, as shown in FIG. 4. In the case of the full-toroidal type continuously variable transmission also, the generated push force Fac is greater than the appropriate push force Fan2, as shown in FIG. 5. In either case, the push force Fac lowers the power transmission efficiency of the continuously variable transmission. In the case of the full-toroidal type, in particular, the transmission efficiency lowers substantially.
In the toroidal type continuously variable transmission described in PCT National Publication No. 6-502476, the hydraulic loading mechanism is used as the push mechanism. The hydraulic loading mechanism comprises a pressure source such as a hydraulic pump, a cylinder rotatable integrally with the input shaft, and the back surface portion of the input disk that serves as a piston portion in the cylinder. The input disk is pressed toward the output disk by means of the pressure of oil that is fed from the pressure source into the cylinder. The transmission described in PCT National Publication No. 6-502476 is provided with only one cylinder and one piston portion.
A push force that is generated by the hydraulic loading mechanism is controlled to be at an appropriate value by means of a well-known control device such as an ECU (engine control unit). This control device obtains the appropriate push force in accordance with the conditions including the input torque, gear ratio, rotational frequency, lubricant temperature, etc. Thus, the power transmission efficiency of the toroidal type continuously variable transmission can be improved by using the hydraulic loading mechanism.
In the push mechanism of the toroidal type continuously variable transmission, however, the push force should be enhanced in proportion to the input torque from the drive source. In the toroidal type continuously variable transmission that uses the hydraulic loading mechanism, therefore, the pressure of the oil to be fed into the cylinder must be increased when the input torque is high. Sealing the high-pressure oil requires the sliding resistance of seal members between the piston portion and the cylinder to be increased, thus entailing a higher power loss. Since the high-pressure oil must be fed into the cylinder, moreover, the pressure source and therefore the toroidal type continuously variable transmission itself are expected to be large-sized.
The pressure of the oil to be fed into the cylinder may possibly be adjusted to a lower level by increasing the pressure receiving area of the piston portion (input disk) on which the oil pressure acts. In this case, however, the size of the toroidal type continuously variable transmission itself increases, and the manufacturing costs of the input disk and the like pile up inevitably.
Accordingly, the object of the present invention is to provide a toroidal type continuously variable transmission, of which the power transmission efficiency can be restrained from lowering and which can be restrained from being large-sized.
In order to achieve the above object, a toroidal type continuously variable transmission according to the present invention comprises an input shaft rotatable by means of a drive source, a first cavity including a first input disk rotatable together with the input shaft and a first output disk opposed to the first input disk in the axial direction of the input shaft, a second cavity including a second input disk rotatable together with the input shaft and a second output disk opposed to the second input disk in the axial direction of the input shaft, a hydraulic loading mechanism including first and second hydraulic chambers arranged in the axial direction of the input shaft and adapted to press one of the disks in the first cavity toward the other so that the input and output disks approach each other when pressurized oil is fed into the hydraulic chambers, and an interlocking portion adapted to shift one of the disks of the second cavity toward the other as the one disk of the first cavity is shifted toward the other by means of the hydraulic loading mechanism.
The hydraulic loading mechanism of the invention includes the first and second hydraulic chambers that press the input and output disks in the first cavity and the input and output disks in the second cavity toward one another. With use of these hydraulic chambers, the pressure receiving area of a piston portion that is subjected to oil pressure can be widened. Accordingly, the pressure of the oil supplied to the hydraulic chambers can be suppressed, and a pressure source can be restrained from becoming large-sized. Since the sliding resistance of a seal member for sealing the hydraulically-operated piston portion can be lowered, so that the power transmission efficiency can be restrained from lowering. The interlocking portion shifts the input and output disks of the second cavity toward each other as the hydraulic loading mechanism presses the input and output disks of the first cavity so that they approach each other. Thus, push force can be generated in the input and output disks of both the first and second cavities by means of the one hydraulic loading mechanism. In consequence, the toroidal type continuously variable transmission itself can be restrained from becoming large-sized.
Preferably, in the toroidal type continuously variable transmission of the invention, the hydraulic loading mechanism includes a cylinder defining the first hydraulic chamber, a first disk member located inside the cylinder, a second disk member opposed to the first disk member in the axial direction of the input shaft and defining the second hydraulic chamber, an air chamber defined between the first and second disk members, and a communication hole connecting the inside of the air chamber and the outside of the hydraulic loading mechanism. According to this invention, air can be introduced into or discharged from the air chamber when the pressurized oil is supplied to the first and second hydraulic chambers to move the piston portion, so that the piston portion can be moved smoothly. Thus, the responsivity and efficiency of the toroidal type continuously variable transmission are improved.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.